1. Technical Field
The present invention relates to a wavelength conversion element, a method for manufacturing the wavelength conversion element, an illuminator, and a projector.
2. Related Art
In recent years, as an illuminator for a projector, an illuminator using a wavelength converter, such as a rotary fluorescent plate, has been proposed. The rotary fluorescent plate produces fluorescence when a phosphor layer is irradiated with excitation light in a state in which a substrate on which the phosphor layer is provided is rotated. The rotary fluorescent plate thus produces illumination light containing the fluorescence.
JP-A-2016-70947 discloses a “wavelength conversion element” including a substrate, a reflector provided on the substrate, a wavelength conversion layer provided on a surface of the reflector that is the surface opposite the substrate, and a reflection surface provided between the reflector and a surface of the wavelength conversion layer that is the surface opposite the reflector and totally reflecting fluorescence incident on the reflection surface at angles of incidence greater than or equal to the critical angle associated with the reflection surface. JP-A-2016-70947 further discloses a configuration in which an intermediate layer made, for example, of a silicone resin having a refractive index smaller than the refractive index of the wavelength conversion layer is provided between the wavelength conversion layer and the reflector.
JP-A-2014-192127 discloses a “fluorescence light source apparatus” including an excitation light source, a wavelength conversion member that converts excitation light from the excitation light source in terms of wavelength into fluorescence, and a base that supports the wavelength conversion member, with a fluorescence reflection surface provided on a surface of the wavelength conversion member that is the surface facing away from the surface on which the excitation light is incident. JP-A-2014-192127 further discloses a configuration in which a fluorescence reflection mirror provided on the base is separate from the wavelength conversion member and an air layer is provided between the fluorescence reflection mirror and the wavelength conversion member.
The wavelength conversion elements described in JP-A-2016-70947 and JP-A-2014-192127 are each a wavelength conversion element in which the fluorescence produced in the wavelength conversion layer is reflected and extracted out of the wavelength conversion element or what is called a reflective wavelength conversion element. In a wavelength conversion element of this type, a reflection surface that reflects the fluorescence is provided on a side of the wavelength conversion layer that is the side opposite the excitation light incident surface. The wavelength conversion element, however, has a problem of a fluorescence loss that occurs when the fluorescence is reflected off the reflection surface, resulting in a decrease in light emission efficiency.